We have confirmed the report, demonstrating an increase in the specific activity of p60c-src protein-tyrosine kinase as found in human colon carcinoma cell lines. Ten colon carcinoma cell lines were examined and all were found to exhibit dramatic increase in p60c-src kinase activity, as compared to colon control lines. The oncogenic potential of c-src may be activated by a decrease in the phosphorylation state of the Tyr 527 residue, or by one or more mutations in the gene. The specific aims of this Phase I proposal are (i) to determine whether there is a decrease in the activity of a protein-tyrosine kinase which phosphorylates the Tyr 527 site in p60c-src; (ii) to determine whether there is an increase in the activity of a phospho-tyrosyl protein phosphatase which dephosphorylates the p60c-src Tyr 527 site; and (iii) to determine whether one or more mutations in the src genome are responsible for the activation of p60c-src, and if so, to map such a site(s). In Phase II we propose to purify to homogeneity the specific protein responsible for c-src activation in human colon carcinomas and generate monoclonal antibodies against this protein species. These antibodies could potentially be diagnostic reagents for detection of human colon carcinomas.